Purdue OWL
This is like having 24/7 tutorial help. Whatever you want to know - how to use semicolons, if you need to use affect or effect, why the teacher keeps marking "comma splice" on your writing - you can come here and look it up. You'll get concise explanations of grammar and punctuation "rules," examples to follow and even quizzes you can use to check you understanding. OWL stands for Online Writing Lab; many universities offer OWL websites, but the Purdue OWL is one of my favorites for ease of use and thorough content.

Citation Machine
This site will help you format citations for MLA, APA, Chicago and Turabian (currently under construction). It's not PERFECT, but at least it will help creat consistency in your citations. For some instructors - close counts.

The Modern Language Association
"The style recommended by the association for preparing scholarly manuscripts and student research papers concerns itself with the mechanics of writing, such as punctuation, quotation, and documentation of sources. MLA style has been widely adopted by schools, academic departments, and instructors for nearly half a century." at Purdue receives over 50,000,000 visits per year, with usage increasing steadily each month."